Facial animation method

ABSTRACT

A 3D imaged head consisting of a set of meshes is animated by modelled facial muscles. For natural animation of the lips in speech, the lower and upper lips are distinguished in a set of lip mesh based on the nodes of the mesh on a boundary of the lip corner and mouth opening, and lower and upper zones of the head are divided by the boundary. Modelled muscles attached to the upper lip, with intersecting zones of influence in the upper zone, and attached to the lower lip, with intersecting zones of influence in the lower zone, displace nodes of mesh respectively in the upper lip and under the nose and in the lower lip and the chin. Other muscles have zones of influence in the lower and upper zones.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of animating faces in threedimensions used in a data processing means including an engine foranimating the head of a speaker previously stored and analyzed. Forexample, the data processing means relates to teleconferencing,teleworking or collaborative work, or intelligent agents for reading outpages of electronic mail, or virtual assistants with applications toe-commerce.

2. Description of the Prior Art

In the prior art, most animation engines are not muscular and the faceis often animated by morphing between key expressions of the headproduced manually by artists. Muscular animation engines are generallymore comprehensive but do not take into account the elasticity of theskin, which rules out real time animation of the head.

A muscular animation engine is of interest because of the ease withwhich it can describe an animation as a set of muscular contractions,the head being structured in terms of predetermined sets of meshes, forexample the lips, the eyes, the eyelids, etc. These sets of contractionscan often be generalized from face to face. For example, a smile isalways obtained by contraction of the zygomaticus muscles acting on thecorners of the lips.

For example the following papers by Keith WATER: “A Muscle Model forAnimating Three-Dimensional Facial Expression”, Computer Graphics, vol.21, no. Jul. 4, 1987, pages 17-24, and “Analysis and Synthesis of FacialImage Sequences Using Physical and Anatomical Models”, IEEE Transactionson Pattern Analysis and Machine Intelligence, No. 6, pages 569 to 579,Jun. 15, 1993, suggest animating the face by means of musclemobilization in the form of a vector within an angular influence sectorwithin which a mesh node is moved as a function of an angularattenuation factor and a radial attenuation factor.

However, in the above type of animation engine, the lips are dissociatedand the mouth is opened by rotation of the lower jaw fastened to thelower lip. This rotation destroys the corners of the lips, which doesnot reflect accurately the independent movement of the lips whenspeaking.

OBJECT OF THE INVENTION

The present invention aims to improve animation of the lips, withoutmaking it overcomplex, and so that it reproduces more faithfully thecorresponding real movement of the lips and is executed in real time.

SUMMARY OF THE INVENTION

Accordingly, a method of animating a head imaged in three dimensions andacquired in a data processing means in the form of sets of meshesincluding a set of lips, by means of modelled facial muscles, ischaracterized in that it includes the steps of:

-   -   distinguishing lower and upper lips in the set of lips as a        function of mesh nodes at the level of a lip corner and a mouth        opening boundary,    -   determining upper and lower zones of the head substantially        shared by at least the boundary, and    -   constituting a first group of modelled muscles extending toward        the upper lip and having zones of influence intersecting at        least two by two situated in the upper zone for displacing mesh        nodes in the upper lip and under the nose of the head, a second        group of modelled muscles extending toward the lower lip and        having zones of influence intersecting at least two by two        situated in the lower zone for displacing mesh nodes in the        lower lip and in the chin of the head, and a last group of        modelled muscles having zones of influence for displacing each        of the mesh nodes in the upper and lower zones in order to        stretch and contract the lips.

Thanks to the distribution of muscles modelled in the first, second andthird groups independent with respect to each other and to the influenceof at least two muscles on certain mesh nodes, the speaking mouth opensin a more natural manner.

As will become clear later, the invention also provides parametricanimation through determining parameters for animating at least one ofthe following organs: an eye, an eyelid, a lower jaw, a neck.

The invention also relates to client-server systems relating toanimation of the face. According to a first embodiment, the clientincludes a data processing means having acquired a head imaged in threedimensions in the form of sets of meshes and parameters by the methodaccording to the invention, for animating the head as a function ofanimation commands. The server is a processing server for convertingresponses read in a database addressed by requests corresponding tomessages transmitted by the client into messages and animation commandstransmitted to the client.

According to a second embodiment of the client-server system, the serveris a database server and the client includes a data processing means anda conversational means. The processing means has acquired a head imagedin three dimensions in the form of sets of meshes and parameters by themethod according to the invention, for animating the head as a functionof animation commands. The conversational means converts responses readin the database server addressed by requests corresponding to messagesprovided in the client into messages applied in the client and animationcommands transmitted to the data processing means.

The sets of meshes and the parameters are preferably selected andacquired from a predetermined server.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become moreclearly apparent on reading the following description of a plurality ofpreferred embodiments of the invention, with reference to thecorresponding accompanying drawings, in which:

FIG. 1 is a meshed front view of a head;

FIG. 2 is a meshed side view of the head;

FIG. 3 is an algorithm of the facial animation method in accordance witha preferred embodiment of the invention;

FIG. 4 is a meshed front view of the lips of the head;

FIG. 5 is an algorithm for distinguishing between the upper and lowerlips;

FIG. 6 is a front view analogous to FIG. 1, without the hair, showingthe location of facial muscles;

FIG. 7 is a table indicating the functions of the facial muscles shownin FIG. 6 and controlling the movement of the lips, as well as zones ofinfluence of these muscles relative to the upper and lower zones;

FIG. 8 is an algorithm included in the FIG. 3 algorithm for determiningupper and lower zones of the head;

FIG. 9 is a view analogous to FIG. 1, without the hair, showing theseparation between the upper and lower zones at the level of the lips;

FIG. 10 is a graph of the zone of influence of a muscle and is used toexplain the displacement of mesh nodes when the muscle contracts;

FIGS. 11A and 11B are graphs of a meshed zone of influence when thecorresponding muscle is contracted 20% and 60%, respectively;

FIG. 12 is a table indicating the functions of the frontal muscles shownin FIG. 6 and zones of influence of these muscles relative to the upperand lower zones;

FIGS. 13A and 13B show the influence of three muscles, respectivelyafter a 20% contraction and a 60% contraction, on the displacements ofmesh nodes common to their zones of influence, in order to demonstratethe impossibility of displacing mesh nodes that the invention avoids;

FIG. 14 is a table of the distribution of facial muscles into groups inview of their additive or independent contribution to mesh nodedisplacements;

FIGS. 15 and 16 are graphs in axial section of a variant ellipsoid-basedzone of influence of a muscle, respectively in a plane containing thevector modelling the muscle and in a plane perpendicular to that vector;

FIG. 17 is an algorithm for determining parameters for animating eyes,eyelids, a lower jaw and a neck of the head; and

FIGS. 18 and 19 are block diagrams of two embodiments of a client-serversystem for facial animation in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The facial animation method according to the invention is used in ananimation engine implemented in a data processing means which isinstalled, for example, in a personal computer, a multimedia Internetserver, or a teleconferencing or teleworking terminal which has receivedthe three-dimensional image of the head TE of a speaker facing theterminal in order to transmit it to the terminal of a remote speakerduring the teleconference. In another variant, a virtual assistantinstalled in a public terminal providing access to databases, forexample shopping and tourist information databases, has stored thethree-dimensional image of the head TE of an operator-receptionist inorder to display it while information is being listened to. As shown inFIGS. 1 and 2, respectively in front view in a plane XOY and inright-hand side view in a plane YOZ, the head TE of the speaker or theoperator has been acquired by the data processing means in the form of athree-dimensional meshed image produced by a scanner or deduced from oneor more photographs of the head analyzed by software that is not part ofthe invention.

In an initial step E0, the head TE is defined superficially by aplurality of sets of polygonal (essentially triangular andquadrilateral) meshes in which respective animations can be applied.However, the bust BU covered by garments are generally not animated. Thesets of triangular meshes include particularly the facial epidermis, thelips LE, the right and left upper eyelids PD and PG, and the whites BOGand BOD of the left eye and the right eye, for example.

In the remainder of the description, S_(i) and S_(j) designate any twomesh nodes.

As shown in FIG. 3, the facial animation method implemented in the formof software in the data processing means includes the initial step E0relating to the superficial meshing of the face in three dimensions, asdescribed previously, followed by steps E1 to E5 specific to theinvention. The method allows real time automatic animation of the head,and in particular of the face, of the speaker or operator, as a functionof an analysis of their voice or a text, so as to translate phonemesinto animation of the face of the speaker or operator. Movement of thelips is essential for this animation.

FIG. 4 shows in detail the set of triangular meshes LE comprising alower lip LI and an upper lip LS, as seen in front view by projectingthe set along the axis OZ onto the plane XOY. In accordance with theinvention, the step E1 distinguishes the lower lip LI and the upper lipLS, by means of the algorithm shown in FIG. 5, in order to animate thelips separately. This lip distinction algorithm comprises steps E11 toE18. In an initial step E10 included in step E0, all the coordinates ofthe nodes of the triangular meshes of the set LE are known.

In the first step E11, the mesh nodes S_(i) at the internal periphery ofthe set LE are identified to define the interior contour C_(in) of theset of lips LE surrounding a slight opening of the mouth BO between thestationary lips and the corners at the ends of the lips. The mesh nodesat the external periphery of the set LE are identified to define theexterior contour C_(ex) of the set LE of upper and lower lips passingthrough the corners of the lips.

In step E12, the laterally outermost nodes S_(ing) and S_(ind) along theabscissa axis OX, i.e. the leftmost and rightmost nodes, are detected onthe interior contour C_(in). Likewise, in step E13, the laterallyoutermost nodes S_(exg) and S_(exd) along the abscissa axis OX, i.e. theleftmost and rightmost nodes, are detected on the exterior contourC_(ex); another node S_(inf) corresponding to the smallest ordinate onthe exterior contour C_(ex) is also detected.

The pairs of left-hand nodes (S_(ing), S_(exg)) and right-hand nodes(S_(ind), S_(exd)) thus materialize the left and right corners of thelips.

Then all the mesh nodes to the left of the left node S_(ing) of theinternal contour in FIG. 4 and having an ordinate Y less than the leftcorner segment S_(exg) S_(ing) having the ends previously detected aremarked in step E14 as being nodes belonging to the lower lip LI.Likewise, all the mesh nodes to the right of the right-hand node S_(ind)of the internal contour in FIG. 4 and having an ordinate Y less than theright corner segment S_(exd) S_(ind) having the ends previously detectedare marked in step E15 as being nodes belonging to the lower lip LI.Accordingly, in step E14 and E15 the mesh nodes below one of the cornersegments S_(exg) S_(ing) are marked as belonging to the lower lip LI.

In the next step E16, the lower node S_(inf) is marked as being a nodebelonging to the lower lip LI.

In step E17, all the mesh nodes that have not been marked, i.e. that arenot at the level of the mouth opening BO and have an abscissa X betweenthe abscissae of the nodes of the internal contour of the lips S_(ing)and S_(ind), starting with two nodes near the lower node S_(inf) of thelower lip LI and progressively inundating the lower lip, out to the lipcorner segments, are marked recursively as belonging to the lower lipLI, until there are no more nodes to be marked.

Then, in step E18, all of the other nodes that have not been marked inthe set of lips LE and that do not belong to the lower lip LI are markedas belonging to the upper lip LS. At this stage, the upper and lowerlips LI and LS are separately defined by two sets of mesh nodesseparated by the slight mouth opening OB between the lips and possiblyby boundary points at the level of the corners considered to belong tothe upper lip LS.

Referring to FIG. 3, the facial animation method continues with steps E2and E3 for positioning and defining specialized facial muscles foropening the mouth which are modelled in a particular way and determininga lower zone ZI and an upper zone ZS in the head TE in order to limitthe action of the specialized muscles and control independent animationof one lip relative to the other lip and thereby separation of the lipsLI and LS.

As shown in FIG. 6 and set out in the FIG. 7 table, step E2 defines agroup of 17 muscles controlling the movement of the lips in an areawhich is situated substantially under the nose and is symmetrical withrespect to an anterior-posterior median plane AP of the head TE. As analternative to this, step E2 can be executed after the initial step E0.The seventeen muscles are:

-   -   left and right internal nasal-labial muscles M1G and M1D        extending obliquely downward along the alae of the nose;    -   a central labial levator muscle M2 whose attachment point is        situated under the septum of the nose and which extends downward        to the sub-nasal groove S_(sup) of the upper lip LS (FIG. 4);    -   left and right internal nasal-labial muscles M3G and M3D whose        attachment points are substantially at the root of the nostrils        and extend substantially vertically downward to the external        contour C_(ex) substantially between the node S_(sup) marking        the sub-nasal groove and the corners of the lips;    -   left and right large zygomaticus muscles M4G and M4D attached        substantially above the respective ears and extending obliquely        substantially as far as the external nodes S_(exg) and S_(exd)        at the corners of the lips;    -   right and left risorius muscles M5G and. M5D extending        substantially horizontally from the middle of the cheeks to the        external nodes at the corners of the lips;    -   left and right angular depressor muscles M6G and M6D extending        substantially obliquely upward and laterally of the chin to the        external nodes at the corners of the lips;    -   left and right triangular muscles M7G and M7D extending        substantially vertically upward from the eminences of the chin        to the external contour C_(ex) of the lower lip LI between the        lower node S_(inf) and the external nodes at the corners of the        lips;    -   a chin muscle M8 extending vertically from the cleft of the chin        to the lower node S_(inf) of the lower lip LI;    -   right, left and front orbicularis muscles M9G, M9D and M9F which        have attachment points at the middle MO (FIG. 4) of the mouth        opening which is situated between the facing central nodes on        the internal contour C_(in) and which are respectively directed        toward the nodes S_(ing) and S_(ind) of the segment of the mouth        opening OB and horizontally toward the interior of the mouth.

The three orbicularis muscles M9G, M9D and M9F constitute an annularmuscle which acts as a sphincter around the mouth, centered on themiddle MO, for example to simulate the enunciation of the letter O.

In accordance with the invention, the actions of the seventeen modelledmuscles listed above and specializing in opening the mouth, to be morespecific in animating the lips, are limited to respective determinedzones of influence to enable separation of the lips. To obtain thisseparation, step E3 defines a lower zone ZI of the face and an upperzone ZS of the face in order to limit the action of some of thesemuscles to respective nodes of one or both zones ZI and ZS, as indicatedin the right-hand column of the FIG. 7 table.

As shown in detail in FIG. 8, which relates to FIG. 9, one of the twozones ZI and ZS, for example the lower zone ZI, is determined by fivesteps E31 to E35.

In step E31, all the mesh nodes S_(i) of the lower lip LI in the set ofmeshes LE are marked as belonging to the lower zone ZI of the face. Instep E32, the middle MB of the mouth is determined as being the middleof the segment between the external nodes S_(exg) and S_(exd) at thecorners of the lips detected previously, in step E13 (FIG. 5), as beingthe outermost nodes on the exterior contour C_(ex). Left and right jawpivot axis nodes S_(pg) and S_(pd) are determined in step E33substantially at the base of the ears to mark a horizontal pivoting axisof the jaws, in particular of the lower jaw, as shown in FIG. 2.

In the next step E34 all the mesh nodes S_(i) of the head and inparticular of the set of surface meshes referred to as the “facialepidermis”, situated under the segment S_(pg) S_(exg) on the left-handprofile projection (not shown) for the nodes to the left of the middleMB of the mouth, i.e. to the left of the anterior-posterior median planeAP of the head TE, are marked as belonging to the lower zone ZI.Similarly, all the nodes of the “facial epidermis” set of meshessituated under the segment S_(pd) S_(exd) on the right-hand profileprojection shown in FIG. 2, for the nodes to the right of the middle MBof the mouth, i.e. to the right of the anterior-posterior median planeAP of the head TE, are marked as belonging to the lower zone ZI. Thelower zone is therefore situated under a broken line joining the pivotaxis nodes S_(pg) S_(pd) through the segment between the external cornernodes S_(exg) and S_(exd).

Then, in step E35, all the other mesh nodes of the head, in particularof the “facial epidermis” set, are marked as belonging to the upper zoneZS of the head.

In FIG. 9, the shaded mesh portion represents the lower zone ZI and theunshaded mesh portion represents the upper zone ZS.

As shown in the left-hand column of the FIG. 7 table, which relates toFIG. 6, the muscles M2, M3G and M3D above the upper lip LS are operativeonly in the upper zone ZS and the muscles M7G, M7D and M8 under thelower lip LI are operative only in the lower zone ZI, to move the lipstoward and away from each other. The other muscles of the FIG. 7 tablesituated laterally of the mouth each move mesh nodes in the lower andupper zones at the same time to stretch and contract the lips laterallyor obliquely.

The invention adopts a muscular model, shown in FIG. 10, somewhatsimilar to that recommended by WATERS, taking account of the elasticityof the skin in the muscular contraction itself, which avoids long andfastidious computations.

A modelled muscle is attached to the meshed head by only two points,very often coinciding with mesh nodes, and which are represented by theorigin and the oriented extremity of a muscle vector

$\overset{\rightarrow}{AI}.$The origin of the vector constitutes a point of attachment A of themuscle considered as the root of the muscle, since from a biologicalpoint of view it is attached to the bones of the head TE. The orientedextremity constitutes a point of insertion I of the muscle into thetissue. During contraction, the point of attachment A and the point ofinsertion I remain stationary and the muscle acts like a convergentmagnetic field, attracting the mesh nodes S_(i) situated in a conicalzone of influence ZN near the vector

$\overset{\rightarrow}{AI}$in the direction of the origin A of the vector, as can be seen in FIGS.11A and 11B for 20% and 60% contractions of the muscle modelled inaccordance with the invention. The zone of influence ZN of the musclecorresponds to a circular cone with generatrices AB, an axis along thevector

$\overset{\rightarrow}{AI},$a cone angle α and a spherical base BB with center A. The conical zoneof influence ZN contains the whole of the vector

$\overset{\rightarrow}{AI},$as shown in FIG. 10.

The modelled muscle vector

$\overset{\rightarrow}{AI}$in the zone of influence ZN is defined by the following parameters:

-   -   a circular aperture angle α which defines, for an angle        β=IAS_(i)relative to the direction of the vector of displacement

$\overset{\rightarrow}{\delta\; S_{i}}$of a mesh node S_(i) relative to the axis AI of the zone of influenceZN, the limit not to be exceeded for the node S_(i) to be moved in thezone of influence ZN of the muscle upon contraction thereof;

-   -   a zone of angular and radial attenuation AAR of the contraction        of the muscle delimited by a frustum of a cone with generatrices        TB and concentric spherical bases TT and BB, situated at the        spherical periphery of the zone of influence ZN and containing        the oriented extremity I of the vector

$\overset{\rightarrow}{AI}$with a predetermined width TB within which the mesh nodes S_(i) aremoved by the muscle more and more when the node S_(i) is situated nearthe point of intersection I′ of the muscular segment AI and the smallerbase TT;

-   -   a zone of angular attenuation AA of the contraction of the        muscle delimited by a cone between the node A and the smaller        base TT, inside which the mesh nodes S_(i) are moved by the        muscle more and more when the node S_(i) is situated near the        muscle segment AI and the node A.

The nodes S_(i) on the periphery of the zone of influence ZN, i.e. onthe conical surface with generatrix AB and on the spherical larger baseBB, are stationary during contraction of the muscle. If the angleβ=IAS_(i) increases until it is equal to the angle α, an attenuation δof the displacement is more and more dominant (δ≈0), which prevents anexaggerated boundary appearing between the nodes that are displaced andtheir neighbors that are not. The displacement of a mesh node S_(i) iscomputed by adding a displacement vector

$\overset{\rightarrow}{\delta\; S_{i}}$in the opposite direction to the vector

$\overset{\rightarrow}{A\; S_{i}}$to the coordinates X, Y, Z of the node S_(i) in accordance with thefollowing equation:

${\overset{\rightarrow}{\delta\; S_{i}} = {{- C} \cdot \delta \cdot {\overset{\rightarrow}{AS}}_{i}}},$

-   -   in which C is a percentage of contraction of the muscle and δ is        an attenuation coefficient equal to the product of an angular        attenuation coefficient δ_(A) and a radial attenuation        coefficient δ_(R), which are defined as follows:

$\delta_{A} = \frac{{\cos\;\beta} - {\cos\;\alpha}}{1 - {\cos\;\alpha}}$δ_(R)=cos((∥T′S _(i) ∥/∥TB∥)  (π/2))

-   -   where δ=δ_(A)·δ_(R) if ∥AS_(i)∥>∥AT∥    -   and δ=δ_(A) and δ_(R)=1 if ∥AS_(i)∥≦∥AR∥,    -   and T′ is the intersection of AS_(i) with the base TT.

The attenuation coefficient δ_(A) is specific to the invention anddepends on the angular distance β between the vectors

${\overset{\rightarrow}{AS}}_{i}$and

$\overset{\rightarrow}{A\; I}.$The maximum contraction, i.e. the contraction when

${\overset{\rightarrow}{\delta\; S_{i}} = {{- C} \cdot {\overset{\rightarrow}{AS}}_{i}}},$is obtained uniquely for the nodes included in the segment AI′ where β0and δ_(A)=δ=1, the point I′ being the node that can be displacedfarthest. The attenuation coefficient δ_(R) is a function of the radialdistance between the points S_(i) and T′ and varies only in thefrustoconical area AAR, between 0 and 1 and from the smaller base TTtoward the larger base BB.

As can also be seen in FIG. 6, other modelled facial muscles located onthe forehead are provided for animating the left and right eyebrows SGand SD. The modelled muscles listed in the FIG. 12 table are:

-   -   left and right external frontal muscles M10G and M10D, left and        right frontal muscles M11G, M11D, and left and right large        frontal muscles M12G and M12D which are attached to the forehead        and respectively extend downward substantially as far as the        external, middle and internal extremities of the left and right        eyebrows SG and SD;    -   left and right lateral corrugator muscles M13G and M13D which        are attached substantially laterally to the top of the nose and        directed upward, respectively as far as the left and right        eyebrows, between the points of attachment of the muscles        M11G-M12G and M11D-M12D;    -   left and right lower orbicularis muscles M14G and M14D and left        and right upper orbicularis muscles M15G and M15D which are        respectively attached to the external corners of the eyes and to        the middle of the upper eyelids PAG and PAD, and which        respectively extend upward substantially toward the external        extremities of the eyebrows and downward substantially toward        the middles of the lower eyelids, to lower the exterior        extremities of the eyebrows and raise the eyelids.

As already stated, when a muscle acts on a mesh node S_(i), it generatesa displacement vector {right arrow over (δS_(i))} which must be added tothe coordinates of the node S_(i) to obtain the displaced node. However,if a mesh node S_(i) is situated in more than one intersecting zones ofinfluence of muscle, and is therefore subjected to the action of allthose muscles, adding displacement vectors without taking appropriateprecautions may generate an exaggerated displacement of the mesh noderesulting from the addition of the vectors. The displaced node may beattracted farther than the points of attachment of the modelled musclesthat contribute to the displacement.

For example, three muscles

${\overset{\rightarrow}{A_{1}I}}_{1},{\overset{\rightarrow}{A_{2}I}}_{2}$and

${\overset{\rightarrow}{A_{3}I}}_{3}$have intersecting zones of influence ZN₁, ZN₂ and ZN₃ shown in FIG. 13A.The muscle vectors of these three muscles meet at a common mesh node SC.The addition of the action of these three vectors on the common meshnodes, such as the node SC, common to the three zones of influence, witha contribution of C=20% for each of them, keeps the displaced nodesSC_(A) in the zones of influence. On the other hand, if the percentageof contraction C is higher, for example equal to 60%, as shown in FIG.13B, applying resultant vectors obtained by adding the contributions ofthe three muscles A₁I₁, A₂I₂ and A₃I₃ to the common mesh nodes, such asthe node SC, generates displaced nodes SC_(B) that are drawn out of thezones of influence ZN₁, ZN₂ and ZN₃, which is impossible in practice.

To overcome this problem, step E4 classifies the modelled facial musclesto constitute groups G1 to G5 according to their orientation, as shownin the FIG. 14 table.

The first group G1 comprises the muscles M2, M3G, M3D, M4G and M4Dattached to the upper lip LS and having zones of influence intersectingat least two by two between adjoining muscles to displace mesh nodesS_(i) in the lip LS and under the nose NE. The second group G2 comprisesthe muscles M6G, M6D, M7G, M7D and M8 attached to the lower lip LI andhaving zones of influence intersecting at least two by two betweenadjoining muscles to displace mesh nodes S_(i) in the lip LI and thechin ME. The third group G3 comprises the left frontal muscles M10G,M11G, M12G and M15G situated substantially in the left frontal portionand having zones of influence intersecting at least two by two, in ananalogous manner to FIG. 13A, to displace frontal mesh nodes S_(i)substantially in and/or above the eyebrow SG and/or the eyelid PAG.Similarly, the fourth group G4 comprises the right frontal muscles M10D,M11D, M12D and M15D respectively symmetrical to the muscles M10G, M11G,M12G and M15G.

In each of the first four groups G1, G2, G3 and G4, the displacementvector of a mesh node S_(i) is determined by adding the displacementvectors resulting from the action of the muscles of the group able toact on the mesh node S_(i) to obtain a resultant vector which is thentruncated so that the modulus of the resultant vector is equal to thehighest modulus of the displacement vectors of the muscles that have toact.

For example, if the aforementioned three muscles A₁I₁, A₂I₂ and A₃I₃shown in FIGS. 13A and 13B belong to one of the four groups G1 to G4 andhave zones of influence ZN₁, ZN₂ and ZN₃ containing in common at leastone mesh node S_(i), for example like the muscles M3D, M2 and M3G in thefirst group G1, or the muscles M7D, M8 and M7G in the second group G2,the node S_(i) is displaced in accordance with the invention by a vectorhaving the same direction as the resultant vector equal to the sum ofthe displacement vectors

$\overset{\rightarrow}{\delta\; S_{i1}},\overset{\rightarrow}{\delta\; S_{i2}}$and

$\overset{\rightarrow}{\delta\; S_{i3}}$of the three muscles, in other words:

$\begin{matrix}{\overset{\rightarrow}{\delta\; S_{i}} = {\overset{\rightarrow}{\delta\; S_{i1}} + \overset{\rightarrow}{\delta\; S_{i2}} + \overset{\rightarrow}{\delta\; S_{i3}}}} \\{\overset{\rightarrow}{\delta\; S_{i}} = {{{- C_{1}} \cdot \delta_{1} \cdot \overset{\rightarrow}{{A\;}_{1}S_{i}}} - {C_{2} \cdot \delta_{2} \cdot \overset{\rightarrow}{{A\;}_{2}S_{i}}} - {C_{3} \cdot \delta_{3} \cdot \overset{\rightarrow}{{A\;}_{3}S_{i}}}}}\end{matrix}$and having the same modulus as the vector

$\overset{\rightarrow}{\delta\; S_{i}}$if:

${\overset{\longrightarrow}{{\delta S}_{i}}} \leq {\sup\left( {{\overset{\longrightarrow}{{\delta S}_{i1}}},\;{\overset{\longrightarrow}{{\delta S}_{i2}}},\;{\overset{\longrightarrow}{{\delta S}_{i3}}}}\; \right)}$and a modulus equal to the highest of the three moduli, denoted “sup”,otherwise. In the foregoing equations, C₁, C₂ and C₃ designaterespective contractions of the three muscles A₁I₁, A₂I₂ and A₃I₃, andδ₁, δ₂ and δ₃ designate attenuation coefficients respectively dependingon the location of the node S_(i) in the zones of influence ZN₁, ZN₂ andZN₃.

The last group G5 comprises various muscles and in particular modelledmuscles M4G, M4D, M5G, M5D, M6G, M6D, M9G, M9D and M9F having zones ofinfluence for displacing each of the nodes which are partly in the upperzone ZS substantially above the lower lip LI and partly in the lowerzone ZI substantially below the upper lip LS, which enables thesemuscles to stretch and contract the lips.

The group G5 also comprises muscles which are chosen so that either anode can be in the zone of influence of only one muscle or thedisplacements are orthogonal. The group G5 thus comprises modelledmuscles M5G and M5D respectively attached to the corners of the lipsS_(exg) and S_(exd) and having independent zones of influence forrespectively and independently displacing mesh nodes in oppositedirections toward the exterior of the corners of the lips S_(exg) andS_(exd), and modelled muscles M9G, M9D and M9F attached to the middle ofthe mouth and having independent zones of influence for respectively andindependently displacing mesh nodes toward the corners of the lipsS_(exg) and S_(exd) and toward the inside of the mouth.

As an alternative to the above, a modelled muscle vector

${\overset{\longrightarrow}{AI},}\;$whose points of attachment are the origin A and the oriented extremity Iof the vector, is defined by parameters in a zone of influence zn withan elliptical base, as shown in FIGS. 15 and 16. The parameters aresubstantially similar to those defined for the zone of influence ZNshown in FIG. 10, and are designated hereinafter by the correspondinglowercase letters. They are, in addition to the two attachment points:

-   -   a displacement “disp” toward the rear of the origin A of the        vector

$\overset{\longrightarrow}{AI}$away from the oriented extremity I, to a point dA such that:

-   -   disp

$\overset{\longrightarrow}{AI} = {A - {dA}}$so that, for short muscles in particular, the forces do not converge ina very dense manner toward the origin A, but seem to converge toward the“rear” point dA;

-   -   two elliptical aperture angles α_(eh) and α_(ev) in the planes        xz and yz due to the elliptical contour sections of the zone of        influence zn perpendicular to the direction of the vector {right        arrow over (AI)}, and to the ellipsoidal base bb terminating the        zone of influence zn in front of the extremity I; if 2h and 2e        denote the major axis and the minor axis of an elliptical        section with center S′_(j) on the vertical axis Z colinear with        the segment AI, and S_(j) a mesh node at the same level as        S′_(j) in the zone of influence zn, the coordinates x and y of        the node S_(j) are such that:        (x ² /h ²)+(y ² /v ²)=1        i.e. with β_(e)=IdAS_(j) relative to the direction of the        displacement vector

${\overset{\longrightarrow}{\delta\; S}}_{j}$of the node S_(j) relative to the axis z of the zone of influence:r ²=(S _(j) S′ _(j))²=1/[sin²β_(e) /h ²+cos²β_(e) /v ²]h=∥dAS′ _(j) ∥tgα _(eh)v=∥dAS′ _(j) ∥tgα _(ev)

-   -   a zone of angular and radial attenuation aar of the contraction        of the muscle delimited by a frustum of a cone with generatrix        tb and concentric ellipsoidal bases tt and bb, situated at the        ellipsoidal periphery of the zone of influence zn and containing        the oriented extremity I of the vector

${\overset{\longrightarrow}{AI},}\;$and with a predetermined width tb within which the mesh nodes S_(j) aredisplaced by the muscle more and more when the node S_(j) is situatednear the point of intersection i′ of the muscular segment AI and thesmaller base tt;

-   -   a zone of angular attenuation aa of the contraction of the        muscle delimited by a frustum of a cone with a smaller base aa        around the origin A and an intermediate base tt, within which        the mesh nodes S_(j) are displaced by the muscle more and more        when the node S_(j) is situated near the muscular segment AI and        the node A.

It will be noted that the conical area having the base aa and the apexdA does not belong to the zone of influence zn.

The nodes S_(j) at the periphery of the zone of influence zn, i.e. onthe conical surface with the generatrix ab and on the spherical largerbase bb, are stationary when the muscle contracts. If the radialdistance S′_(j)S_(j) increases until it is equal to the radius of thecorresponding elliptical section, an attenuation δ_(e) of thedisplacement is more and more dominant (δ_(e)≈0), which prevents anexaggerated boundary appearing between the nodes that are displaced andtheir neighbours that are not. The displacement of a mesh node S_(j) iscomputed by adding a displacement vector

${\overset{\longrightarrow}{\delta\; S}}_{j}$in the opposite direction to the vector

$d{\overset{\rightarrow}{AS}}_{j}$to the coordinates x, y, z of the node S_(j), in accordance with thefollowing equation:

${\overset{\rightarrow}{\delta\; S}}_{j} = {{{- C_{e}} \cdot \delta_{e} \cdot d}{\overset{\rightarrow}{AS}}_{j},}$

-   -   in which C_(e) is a percentage of contraction of the muscle and        δ_(e) is a coefficient of attenuation equal to the product of an        angular attenuation coefficient δ_(eA) and a radial attenuation        coefficient δ_(eR) defined as follows:        δ_(eA)=(r ² −∥S′ _(j) S _(j)∥)/r ²        δ_(eR)=(∥AI∥/∥dAI∥)cos [((∥dAS _(j) ∥−∥dAt′∥)/(∥dAS′ _(j)        ∥−∥dAt′∥))(π/2)]

with δ_(e)=δ_(eA·δ) _(eR) if ∥dAS_(j)∥>∥dAt∥

and δ_(e)=δ_(eA)=∥AI∥/∥dAI∥ and δ_(eR)=1 if ∥dAa∥≦∥dAS_(j)∥≦∥dAt∥

-   -   and t′ the intersection of dAS_(j) with the base tt.

The modelled muscle with zone of influence zn functions in an analogousmanner to the modelled muscle with the zone of influence ZN.

In a hybrid variant, the muscles of the head are defined partly with azone of influence ZN (FIG. 10) and partly with a zone of influence zn(FIGS. 15 and 16).

Facial animation in accordance with the invention also includesparametric animation of other organs such as the eyes and the uppereyelids, the lower jaw and the neck, whose parameters are defined instep E5 (FIG. 5), which is shown as following on from the associationstep E4, although it can be executed before this, for example after theinitial step E0.

In the initial step E0, the sets of meshes relating to the eyes, i.e. tothe whites BOG of the left eye and BOD of the right eye respectivelycontaining the left iris and pupil and the right iris and pupil, andrelating to the left and right eyelids PAG and PAD, are perfectlydefined. The sets BOG, BOD are assumed to be substantially hemispheres,and the sets PAG and PAD portions of a sphere.

To animate a given eye, for example the right eye BOG, a rotation centerRO of the eye and a rotation axis AP of the corresponding eyelid PAD aresearched for in steps E51 and E52 shown in FIG. 15.

Step E51 searches automatically for two mesh nodes S_(i) and S_(j) thatare farthest apart in the set of meshes relating to the white BOG of thecorresponding eye. The two nodes S_(i) and S_(j) that are farthest apartdefine the extremities of a segment forming a diameter of thehalf-sphere of the eye and the middle of the diametral segment joiningthese two nodes defines the rotation center RO of the eye. Step E51 isrepeated for each eye. Since the face at rest is parallel to the planeXOY in a front view and parallel to the plane YOZ in a side view, eacheye can rotate about the respective center RO and around the axes OX andOY to simulate looking upward or downward and/or to the right or to theleft.

Step E52 determines a rotation axis AP of the corresponding upper eyelidautomatically and in a similar fashion, by searching for two mesh nodesS_(i) and S_(j) that are farthest apart in the corresponding set ofmeshes PAD. The rotation axis about which the set of meshes PAD can turnto simulate opening and closing of the eyelid passes through these twomesh nodes. Step E52 is repeated for the other eyelid PAG.

Animation of the lower jaw MA operates on set's of meshes relating tothe facial epidermis.

Step E53 determines mesh nodes with reference to FIG. 2 as:

-   -   two jaw pivot axis nodes S_(pg) and S_(pd) that are generally        coincident in side view (FIG. 2), if they have not been        determined already in step E33 (FIG. 8),    -   a chin node S_(me) situated in the median anterior-posterior        plane of the head TE and substantially at the origin of the chin        cleft, and    -   a head-neck transition node S_(CO) substantially in the        anterior-posterior median plane and at the apex of the angle        between the underside of the chin and the anterior part of the        neck.

These three mesh nodes define a jaw articulation angular sector AM withnodes S_(pd)(S_(pg)) and sides S_(pd) S_(me) (S_(pg) S_(me)) and S_(pd)S_(CO).

Step E54 then determines a predetermined angular sector α_(M) less thanthe jaw articulation sector AM=S_(me) S_(pd) S_(CO)=S_(me) S_(pg)S_(CO), contained in the sector AM from the common lower side S_(pd)S_(CO), as shown in FIG. 2. A node S1 _(CO) is defined at theintersection of the upper side of the angle α_(M) and the chin.

The lower jaw MA is then defined in FIG. 2 by the angular sector AMformed by the sides S_(pd) S_(me) and S_(pd) S_(CO) of the articulationangle AM.

In step E55, the nodes S_(i) of the set of “facial epidermis” meshessubstantially contained within the articulation angular sector AM aremarked as belonging to the jaw MA. The mouth is not affected by therotation of the jaw and is animated only by the muscles already definedwith reference to FIGS. 6 and 7.

The jaw turns about the axis S_(pd) S_(pg) parallel to the axis OX, asshown in FIG. 9. To prevent the jaw MA colliding with the neck CO, therotation of the jaw is progressively retarded in the downward directionfor mesh nodes in the facial epidermis and buccal cavity sets that arewithin the angular sector α_(M), until it becomes zero in the vicinityof the segment S_(pd) S_(CO) The angular segment α_(M) defines the areain which the rotation of the jaw is attenuated.

Subsequently, a rotation β_(M) of the jaw MA, typically of less than 10°or 15°, operates completely (β′=β_(M)) on the mesh nodes S_(i) situatedwithin the angular sector AM−α_(M)=[S_(me) S_(pd) S1 _(CO)] in the upperpart of the articulation sector AM and in an attenuated manner on themesh nodes S_(i) within the angular sector α_(M). When the angulardistance α_(i)=[S_(CO) S_(pd) S_(i)] between the mesh node S_(i) and thelower side S_(pd) S_(me) common to the angular sectors AM and α_(M)decreases, the angular displacement β_(M) of the node S_(i) initiallyprovided for the jaw decreases as a function of an attenuationcoefficient δ_(M) in order for the angular displacement β′_(M) of thenode in the sector α_(M) to be as follows:β′_(M)=β_(M)·δ_(M)

${{with}\mspace{25mu}\delta_{M}} = {{1 - {{\cos\left( {\frac{\alpha_{i}}{\alpha_{M}}\frac{\pi}{2}} \right)}{for}\mspace{20mu} S_{i}}}\; \in {\alpha_{M}.}}$

The neck Co is uniquely a portion of the set of “facial epidermis”meshes. Step E56 determines the neck using the next four nodes of thisset in the anterior-posterior median plane AP of the head:

-   -   upper and lower anterior nodes S_(sup1) and S_(inf1) situated        along the anterior profile of the neck and substantially below        the node S_(CO) and above the origin of the bust BU, and    -   upper and lower posterior nodes S_(sup2) and S_(inf2) along the        posterior profile of the neck and substantially at the level of        the middle MB of the mouth and above the origin of the back.

The next step E57 marks the mesh nodes S_(i) of the set of “facialepidermis” meshes as belonging to the neck CO if they are substantiallybetween the lateral planes passing through the upper nodes S_(sup1) andS_(sup2) and the lower nodes S_(inf1), and S_(inf2). Then, in step E58,all the other nodes of the “facial epidermis” set that do not belong tothe neck, along with all the other nodes in all the other sets of meshesof the head, with the exception of the lower set relating to the bustBU, are explored above the upper anterior node S_(sup1) to be marked asbelonging to the head TE.

Step E59 automatically determines a center of rotation CRT of the headcoinciding with the center of the volume encompassing the mesh nodesbelonging to the neck CO. Although the center of rotation CRT issubstantially in front of the real center of rotation of the head, thevisual effect of the rotation of the head obtained in this way issatisfactory.

The rotation of the head is associated with an attenuation of therotation at the level of the neck between the trace planes S_(sup1)S_(sup2) and S_(inf1) S_(inf2) Step E60 determines minimum and maximumordinates Y_(min) and Y_(max) of the nodes S_(sup1), S_(sup2), S_(inf1)and S_(inf2) defining the neck as a function of the ordinates Y_(sup1),Y_(sup2), Y_(inf1), and Y_(inf2) of these four nodes, such that:Y _(min)=min(Y _(sup1) , Y _(sup2) , Y _(inf1) , Y _(inf2))Y _(max)=max(Y _(sup1) , Y _(sup2) , Y _(inf1) , Y _(inf2))

A subsequent rotation β_(T) of the head TE, typically of less than 10°to 15°, operates completely (β′_(T)=β_(T)) on the mesh nodes situatedabove the lateral plane passing through the upper nodes S_(sup1) andS_(sup2) and in an attenuated fashion on the mesh nodes S_(i) within theneck CO. The closer the mesh node S_(i) to the lateral plane of the neckpassing through the lower nodes S_(inf1), and S_(inf2), the greater theangular displacement β_(T) of the mesh node S_(i) initially provided forthe head TE decreases as a function of the ratio between the differencebetween the ordinate Y_(Si) of the mesh node S_(i) and the minimumordinate and the maximum height (Y_(max)−Y_(min)) of the neck, in orderfor the displacement β′_(T) of the node S_(i) in the neck to be asfollows:β′_(T)=β_(T)·δ_(T)

$\delta_{T} = \frac{\left( {Y_{Si} - Y_{\min}} \right)}{\left( {Y_{\max} - Y_{\min}} \right)}$

Two embodiments of an interactive client-server system for implementingthe facial animation method according to the invention are described byway of example hereinafter.

In a first embodiment intended for teaching, and shown in FIG. 18, theclient CLa is a pupil's microcomputer including an animation module MAaconstituting a processor in which a facial animation engine according tothe invention is implemented. The animation module MAa has previouslyacquired sets of meshes EM and parameters P of the head TE of a“teacher” that are downloaded from a server SE1 offering the pupil aplurality of teacher heads. These sets of meshes and parameters definingthe head of the teacher and downloaded into the module MAa are some orall of the following:

-   -   sets of meshes EM modelling the head of the teacher in three        dimensions using the Virtual Reality Modelling Language (VRML),        and    -   parameters P necessary for defining the parametric and muscular        animations already defined in the foregoing description:    -   jaw: S_(pd)(S_(pg)), S_(me), S_(CO), α_(M) (FIG. 2);    -   neck: S_(inf1), S_(inf2), S_(sup1), S_(sup2) (FIG. 2);    -   muscles (FIGS. 6, 7 and 12): A, I, ZN in FIG. 10 and/or A, I, zn        in the embodiment shown in FIGS. 15 and 16,

where the parameters S_(pd), S_(pg), S_(me), S_(CO), S_(inf1), S_(inf2),S_(sup1), S_(sup2), A and I are mesh nodes each marked by a mesh numberand a mesh node number,

AT and AB and/or dAt and dAb are expressed as fractions of the modulusof the vector

$\overset{\rightarrow}{AI},$and

α_(M), α and/or α_(eh), α_(ev) and β_(e) are angles expressed indegrees.

The server SE2 a of the client-server system of the first embodiment,acting as teacher, comprises a facial animation interface IAF and ascenario base BS. The interface IAF receives QR/CL question or responsedigital messages from the microphone MP or the keyboard KP of the clientCLa and interprets them as requests RQ applied to the base BS, whichselects responses RP in accordance with a predetermined scenario. Aresponse RP is interpreted by the interface IAF in such a manner as tofeed, on the one hand, a QR/SE question or response message to theloudspeaker HP of the client CLa and, on the other hand, animationcommands CA to the animation module MAa to animate the head of theteacher displayed on the screen of the client CLa in harmony with theQR/SE message transmitted.

For example, a professor-pupil application of this embodiment consistsin the pupil revising lessons by exchanging questions-responses with theteacher. In this type of application, the pupil-client CLa remainsconnected to the teacher-server SE2 a throughout the lesson session andis controlled completely by the teacher-server.

The animation commands CA are not tied to the animation engine containedin the module MAa of the client, and control the animation of the headof the teacher as a function of the responses RP supplied by the baseBS. In this first embodiment, the animation commands CA and the QR/CLand QR/SE messages are exchanged between the client CLa and the serverSE2 a via a telecommunication network RT; for example, the server SE2 ais a software application on an Internet site or in a physical server ofan Intranet network. By way of non-exhaustive example, the animationcommands CA relate to all or some of the following facial animations:

-   -   turning the head TE X degrees about the axis OX, Y degrees about        the axis OY and Z degrees about the axis OZ;    -   turning the right eye BOD or the left eye BOG X degrees about        the axis OX and Y degrees about the axis OY;    -   turning the right eyelid PAD or the left eyelid PAG Q degrees        about the respective right or left axis APA;    -   enunciating a text in a synthesized and amplified voice to        produce the corresponding labial animation;    -   enunciating a sound to produce the corresponding labial        animation;    -   choosing a neutral expression for the face of the head; and    -   portraying an emotion, joy or sadness, for example with a        predetermined percentage.

The second embodiment of the client-server system, shown in FIG. 19, ismore localized in hardware terms in a client CLb which is a homecomputer installed in the home of a user. The client CLb also containsan animation module MAb which an animation engine according to theinvention and a second software module called as conversational moduleMC are implemented. The module MC has substantially the same role as thefacial animation interface IAF of the first embodiment, and makes theclient CLb more autonomous than the client CLa. The animation engine haspreviously acquired sets of meshes EM and parameters P defining a headof a receptionist, either during instaflation of the client CLb or bysubsequently consulting the first server SEl. The conversational moduleMC uses artificial intelligence and plays the role of the user's“confidante”. Thus this “confidante” occupies itself with various tasksfor managing the user's home, such as regulating the temperature of theboiler, managing an alarm system and/or participating in maintenance, aswell as collecting information from various servers, such as the serverSE3 shown in FIG. 19. The servers SE3 make available databases BD,including scenario databases, for consulting diverse information, suchas cinema times, weather forecasts, lists of restaurants, etc.

The conversational module MC acquires responses RP to requests RQaddressed to one of the servers SE3 to animate the head of thereceptionist displayed on the screen of the client CLb as a function ofanimation commands CA as defined above, either in real time or off-line.For example, if the user is seeking cinema times or a weather forecast,he formulates a QR/CL message to the conversational module MC via themicrophone MP or the keyboard KP of the client CLb and the module MCimmediately forwards a QR/SE response message to the loudspeaker HP ofthe client CLb with corresponding animation commands CA applied to themodule Mab, if the conversational module has already stored the cinematimes or the weather forecast. If not, the conversational module MAbinterrogates the corresponding server SE3 via a telecommunicationnetwork RT, to read therein the times or forecasts, which will then besent off-line to the user via the animation module MAb so that the usercan consult the cinema times in the evening and the weather forecast onwaking up.

In this second embodiment, the hardware client CLb has a client-serverprocessing model between the modules MAb and MC, and a dataclient-server combination with the server SE3.

The two embodiments of client-server system described aboveadvantageously are free of timing constraints because the animationcommands CA for the animation module MAa, MAb are not predefined butexecuted in real time as a function of QR/SE messages from the “server”IAF, MC. The animation commands are synchronized at the level of theanimation module MAa, MAb of the-client, and not at the server level,which prevents any time lapse between the spoken sound and the animationof the lips.

1. A method of animating, by use of modelled facial muscles, a headimaged in three dimensions and acquired in a data processing arrangementin the form of sets of meshes including a set of lips, said methodincluding the steps of: distinguishing a lower lip and an upper lip insaid set of lips as a function of mesh nodes at the level of a lipcorner and mouth opening boundary, the distinguishing step including:(a) identifying mesh nodes at the periphery of said set of lips todefine an interior contour and an exterior contour of said lips, (b)detecting laterally outermost mesh nodes on said interior contour andexterior contour, (c) marking mesh nodes below one of lip cornersegments defined by the nodes previously detected as belonging to saidlower lip, (d) recursively marking all the unmarked mesh nodes, startingwith nodes near a lower node of said lower lip, as belonging to saidlower lip, and (e) marking all the other unmarked nodes in said set oflips not belonging to said lower lip as belonging to said upper lip,determining an upper zone and a lower zone of said head substantiallyshared by at least a lip corner and mouth opening boundary between themesh nodes belonging to said lower lip and the mesh nodes belonging tosaid upper lip, and providing a first group of modelled musclesextending toward said upper lip and having zones of influenceintersecting at least two by two situated in said upper zone fordisplacing mesh nodes in said upper lip and under a nose of said head, asecond group of modelled muscles extending toward said lower lip andhaving zones of influence intersecting at least two by two situated insaid lower zone for displacing mesh nodes in said lower lip and in achin of said head, and a last group of modelled muscles having zones ofinfluence for displacing each of the mesh nodes in said upper zone andlower zone in order to stretch and contract said lips.
 2. A methodaccording to claim 1, wherein said last group includes modelled musclesextending respectively up to the corners of said lips and havingindependent zones of influence for respectively and independently movingmesh nodes in opposite directions toward the exterior of said corners ofsaid lips.
 3. A method according to claim 1, wherein said last groupincludes modelled muscles attached to the middle of the mouth and havingindependent zones of influence for respectively and independentlydisplacing mesh nodes toward said corners of said lips and toward theinterior of said mouth.
 4. A method according to claim 1, wherein saiddetermining step includes the following steps: determining the middle ofa segment between external nodes as laterally outermost nodes detectedon said exterior contour of said lips, determining jaw pivot axis nodes,marking all the nodes situated under a broken line joining said jawpivot axis nodes through said segment between said external nodes asbelonging to the lower zone, and marking all the other mesh nodes ofsaid head as belonging to the upper zone.
 5. A method according to claim1, wherein a modelled muscle is defined by a conical zone of influencehaving a cone angle α, and a mesh node inside said zone of influence issubjected to a displacement vector that is directed toward the apex ofsaid zone of influence at an angle β to the axis of said zone ofinfluence and which is proportional to an angular attenuationcoefficient δ_(A) defined as follows:$\delta_{A} = \frac{{\cos\;\beta} - {\cos\;\alpha}}{1 - {\cos\;\alpha}}$6. A method according to claim 1, wherein a modelled muscle is definedby a vector having an origin A, an oriented extremity I in afrustoconical zone of influence having an apex dA, and two ellipticalaperture angles, a mesh node S_(j) situated within said zone ofinfluence and at a radial distance S′_(j)S_(j) from the axis of saidzone of influence in an elliptical section of radius r passing throughsaid mesh node S_(j) is subjected to a displacement vector which isdirected toward the node dA of said zone of influence and which isproportional to an angular attenuation coefficient δ_(eA) and to aradial attenuation coefficient δ_(eR) defined as follows:δ_(eA)=(r ² −∥S′ _(j) S _(j) ∥/r ²δ_(eR)=(∥AI∥/∥dAI∥)cos[((∥dAS _(J) ∥−∥dAt′∥)/(∥dAS′ _(j)∥−∥dAt′∥))(π/2)] and δ_(e)=δ_(eA)=∥AI∥/∥dAI∥ and δ_(eR)=1 if∥dAa∥≦∥dAS_(j)∥≦∥dAt∥ where t′ is the intersection of segment dAS_(j)with an intermediate base between a smaller base and a larger base ofsaid zone of influence.
 7. A method according to claim 1, wherein, whena mesh node is situated in a plurality of intersecting zones ofinfluence of muscles, and further including displacing said mesh node bya displacement vector determined by adding displacement vectorsresulting from the action of said muscles in order to obtain a resultantvector and then truncating said resultant vector so that said resultantvector has a modulus equal to the highest modulus of said displacementvectors of said muscles.
 8. A method according to claim 1, wherein thereis included a group of modelled frontal muscles respectively extendingdownward substantially as far as external, middle and internalextremities of eyebrows of said head and to middles of eyelids of saidhead, and having zones of influence intersecting at least two by two todisplace mesh nodes at least in said eyebrows and said eyelids.
 9. Amethod according to claim 1, including a step of determining parametersfor animating at least one of the following organs: an eye, an eyelid, alower jaw, a neck in said head.
 10. A method according to claim 1,including a step of determining a rotation center of an eye of said headas the middle of a segment whose extremities are two farthest apart meshnodes in a set of meshes relating to a white of said eye.
 11. A methodaccording to claim 1, including a step of determining a rotation axis ofan eyelid of said head passing through two farthest apart mesh nodes ina set of meshes relating to said eyelid.
 12. A method according to claim1, including the steps of: determining mesh nodes as jaw pivot axisnodes, a chin node and a head—neck transition node to define an angulararticulation sector AM of jaw, determining a predetermined angularsector α_(M) less than and contained in said articulation sector AM andhaving a lower side common therewith, and marking mesh nodessubstantially contained within said articulation sector AM, in order fora rotation of the jaw to operate completely on mesh nodes situatedwithin an angular sector AM—α_(M) and in an attenuated manner on meshnodes within said angular sector α_(M) so that, if angular distanceα_(i) between a mesh node and said common lower side decreases, saidmesh node is displaced as a function of an attenuation coefficientdefined as follows:$1 - {{\cos\left( {\frac{\alpha_{i}}{\alpha_{M}}\frac{\pi}{2}} \right)}.}$13. A method according to claim 1, including the steps of: determiningupper and lower anterior nodes and upper and lower posterior nodes ● ofa neck of said head; marking mesh nodes substantially contained betweenlateral planes passing through said upper and lower nodes as belongingto said neck; marking all the mesh nodes in said head that do not belongto said neck; determining a center of rotation of said head consistingof the center of a volume encompassing mesh nodes belonging to saidneck; and determining minimum and maximum ordinates Y_(min) and Y_(max)of said upper and lower nodes of said neck, in order for a subsequentrotation of said neck to operate completely on mesh nodes situated abovea lateral plane passing through said upper nodes and in an attenuatedfashion on mesh nodes within said neck so that the closer the mesh nodewith the ordinate Y_(si) to a lateral plane passing through said lowernodes, the greater the angular displacement of said mesh node with saidordinate Y_(si) decreases as a function of a ratio defined as follows:$\frac{\left( {Y_{Si} - Y_{\min}} \right)}{\left( {Y_{\max} - Y_{\min}} \right)}.$14. A client-server system, comprising a client data processingarrangement having a three-dimensional model of a head in the form ofsets of meshes including a set of lips and parameters, and a processingserver for converting responses read in a database addressed by requestscorresponding to messages transmitted by the client into messages andanimation commands transmitted to the client for thereby animating saidhead as a function of said animation commands in said client dataprocessing arrangement, said client data processing arrangement beingarranged for: (a) distinguishing a lower lip and an upper lip in saidset of lips as a function of mesh nodes at the level of a lip corner andmouth opening boundary, the client data processing arrangement beingarranged for distinguishing the lower and upper lip by steps including:(i) identifying mesh nodes at the periphery of said set of lips todefine an interior contour and an exterior contour of said lips, (ii)detecting laterally outermost mesh nodes on said interior contour andexterior contour, (iii) marking mesh nodes below one of lip cornersegments defined by the nodes previously detected as belonging to saidlower lip, (iv) recursively marking all the unmarked mesh nodes,starting with nodes near a lower node of said lower lip, as belonging tosaid lower lip, and (v) marking all the other unmarked nodes in said setof lips not belonging to said lower lip as belonging to said upper lip,(b) determining an upper zone and a lower zone of said headsubstantially shared by at least a lip corner and mouth opening boundarybetween the mesh nodes belonging to said lower lip and the mesh nodesbelonging to said upper lip, and (c) providing a first group of modelledmuscles extending toward said upper lip and having zones of influenceintersecting at least two by two situated in said upper zone fordisplacing mesh nodes in said upper lip and under a nose of said head, asecond group of modelled muscles extending toward said lower lip andhaving zones of influence intersecting at least two by two situated insaid lower zone for displacing mesh nodes in said lower lip and in achin of said head, and a last group of modelled muscles having zones ofinfluence for displacing each of the mesh nodes in said upper zone andlower zone in order to stretch and contract said lips.
 15. Aclient-server system according to claim 14, wherein said sets of meshesare arranged to be selected and acquired from a predetermined server.16. A client-server system according to claim 14, wherein saidparameters define at least animations of a jaw, a neck and muscles ofsaid head.
 17. A client-server system according to claim 14, whereinsaid animation commands relate to at least the following facialanimations of said head: turning said head, turning an eye of said head,turning an eyelid of said head, enunciating a text, enunciating a sound,choosing a neutral expression of the face of said head, portraying anemotion.
 18. A client-server system comprising a database server and aclient data processing arrangement having a head modelled in threedimensions in the form of sets of meshes including a set of lips andparameters for thereby animating said head as a function of animationcommands, said client data processing arrangement being arranged toprovide head animation and simulated conversation, said simulatedconversation being arranged for converting responses read in saiddatabase server addressed by requests of said simulated conversationcorresponding to messages transmitted by said head animation intomessages and animation commands transmitted to said head animation, saidhead animation being arranged for: (a) distinguishing a lower lip and anupper lip in said set of lips as a function of mesh nodes at the levelof a lip corner and mouth opening boundary, the head animation beingarranged for distinguishing the lower lip from upper lip by stepsincluding: (i) identifying mesh nodes at the periphery of said set oflips to define an interior contour and an exterior contour of said lips,(ii) detecting laterally outermost mesh nodes on said interior contourand exterior contour, (iii) marking mesh nodes below one of lip cornersegments defined by the nodes previously detected as belonging to saidlower lip, (iv) recursively marking all the unmarked mesh nodes,starting with nodes near a lower node of said lower lip, as belonging tosaid lower lip, and (v) marking all the other unmarked nodes in said setof lips not belonging to said lower lip as belonging to said upper lip,(b) determining an upper zone and a lower zone of said headsubstantially shared by at least a lip corner and mouth opening boundarybetween the mesh nodes belonging to said lower lip and the mesh nodesbelonging to said upper lip, and (c) providing a first group of modelledmuscles extending toward said upper lip and having zones of influenceintersecting at least two by two situated in said upper zone fordisplacing mesh nodes in said upper lip and under a nose of said head, asecond group of modelled muscles extending toward said lower lip andhaving zones of influence intersecting at least two by two situated insaid lower zone for displacing mesh nodes in said lower lip and in achin of said head, and a last group of modelled muscles having zones ofinfluence for displacing each of the mesh nodes in said upper zone andlower zone in order to stretch and contract said lips.
 19. Aclient-server system according to claim 18, wherein said sets of meshesare selected and acquired from a predetermined server.
 20. Aclient-server system according to claim 18, wherein said parameters arearranged for defining at least animations of a jaw, a neck and ofmuscles of said head.
 21. A client-server system according to claim 18,wherein said animation commands relate to at least the following facialanimations of said head: turning said head, turning an eye of said head,turning an eyelid of said head, enunciating a text, enunciating a sound,choosing a neutral expression of the face of said head, portraying anemotion.
 22. A memory for a client-server system including a databaseserver and a client data processing arrangement having a head modelledin three dimensions in the form of sets of meshes including a set oflips and parameters for thereby animating said head as a function ofanimation commands, the memory being arranged to cause the client dataprocessing arrangement to provide head animation and simulatedconversation, said simulated conversation being arranged for convertingresponses read in said database server addressed by requests of saidsimulated conversation corresponding to messages transmitted by saidhead animation into messages and animation commands transmitted to saidhead animation, said head animation being arranged for: (a)distinguishing a lower lip and an upper lip in said set of lips as afunction of mesh nodes at the level of a lip corner and mouth openingboundary, the head animation being arranged for distinguishing the lowerlip from upper lip by steps including: (i) identifying mesh nodes at theperiphery of said set of lips to define an interior contour and anexterior contour of said lips, (ii) detecting laterally outermost meshnodes on said interior contour and exterior contour, (iii) marking meshnodes below one of lip corner segments defined by the nodes previouslydetected as belonging to said lower lip, (iv) recursively marking allthe unmarked mesh nodes, starting with nodes near a lower node of saidlower lip, as belonging to said lower lip, and (v) marking all the otherunmarked nodes in said set of lips not belonging to said lower lip asbelonging to said upper lip, (b) determining an upper zone and a lowerzone of said head substantially shared by at least a lip corner andmount opening boundary between the mesh nodes belonging to said lowerlip and the mesh nodes belonging to said upper lip, and (c) providing afirst group of modelled muscles extending toward said upper lip andhaving zones of influence intersecting at least two by two situated insaid upper zone for displacing mesh nodes in said upper lip and under anose of said head, a second group of modelled muscles extending towardsaid lower lip and having zones of influence intersecting at least twoby two situated in said lower zone for displacing mesh nodes in saidlower lip and in a chin of said head, and a last group of modelledmuscles having zones of influence for displacing each of the mesh nodesin said upper zone and lower zone in order to stretch and contract saidlips.
 23. The memory of claim 22, wherein said sets of meshes areselected and acquired from a predetermined server.
 24. The memory ofclaim 22, wherein said parameters define at least animations of a jaw, aneck and of muscles of said head.
 25. The memory of claim 22, whereinsaid animation commands relate to at least the following facialanimations of said head: turning said head, turning an eye of said head,turning an eyelid of said head, enunciating a text, enunciating a sound,choosing a neutral expression of the face of said head, portraying anemotion.